Current cytochemical techniques for the investigation of peroxisomes. A review

Giardia intestinalis and its Endomembrane System

Giardia intestinalis has unique characteristics, even in the absence of certain organelles. For instance, Golgi and mitochondria are not found. On the other hand, there is a network of peripheral vacuoles (PVs) and mitosomes. The endoplasmic reticulum (ER), nuclear membrane, peroxisomes, and lipid bodies are present. The peripheral vacuole system seems to play several simultaneous roles. It is involved in the endocytic activity of the trophozoite but also has characteristics of early and late endosomes and even lysosomes, establishing a connection with the ER. Some of the PVs contain small vesicles, acting as multivesicular bodies, including the release of exosomes. The mitosomes are surrounded by two membranes, divide during mitosis, and are distributed throughout the cell. They do not contain DNA, enzymes involved in the citric acid cycle, respiratory chain, or ATP synthesis. However, they contain the iron-sulfur complex and transporters as TOM and TIM. Some mitosomes are linked to flagellar axonemes through a fibrillar connection. During encystation, two types of larger cytoplasmic vesicles appear. One originating from the ER contains the cyst wall proteins. Another contains carbohydrates. Both migrate to the cell periphery and fuse with plasma membrane secreting their contents to give rise to the cell wall.

Impaired mitochondrial medium-chain fatty acid oxidation drives periportal macrovesicular steatosis in sirtuin-5 knockout mice

Medium-chain triglycerides (MCT), containing C8-C12 fatty acids, are used to treat several pediatric disorders and are widely consumed as a nutritional supplement. Here, we investigated the role of the sirtuin deacylase Sirt5 in MCT metabolism by feeding Sirt5 knockout mice (Sirt5KO) high-fat diets containing either C8/C10 fatty acids or coconut oil, which is rich in C12, for five weeks. Coconut oil, but not C8/C10 feeding, induced periportal macrovesicular steatosis in Sirt5KO mice. 14C-C12 degradation was significantly reduced in Sirt5KO liver. This decrease was localized to the mitochondrial β-oxidation pathway, as Sirt5KO mice exhibited no change in peroxisomal C12 β-oxidation. Endoplasmic reticulum ω-oxidation, a minor fatty acid degradation pathway known to be stimulated by C12 accumulation, was increased in Sirt5KO liver. Mice lacking another mitochondrial C12 oxidation enzyme, long-chain acyl-CoA dehydrogenase (LCAD), also developed periportal macrovesicular steatosis when fed coconut oil, confirming that defective mitochondrial C12 oxidation is sufficient to induce the steatosis phenotype. Sirt5KO liver exhibited normal LCAD activity but reduced mitochondrial acyl-CoA synthetase activity with C12. These studies reveal a role for Sirt5 in regulating the hepatic response to MCT and may shed light into the pathogenesis of periportal steatosis, a hallmark of human pediatric non-alcoholic fatty liver disease.

Ultrastructural, Cytochemical, and Comparative Genomic Evidence of Peroxisomes in Three Genera of Pathogenic Free-Living Amoebae, Including the First Morphological Data for the Presence of This Organelle in Heteroloboseans

Peroxisomes perform various metabolic processes that are primarily related to the elimination of reactive oxygen species and oxidative lipid metabolism. These organelles are present in all major eukaryotic lineages, nevertheless, information regarding the presence of peroxisomes in opportunistic parasitic protozoa is scarce and in many cases it is still unknown whether these organisms have peroxisomes at all. Here, we performed ultrastructural, cytochemical, and bioinformatic studies to investigate the presence of peroxisomes in three genera of free-living amoebae from two different taxonomic groups that are known to cause fatal infections in humans. By transmission electron microscopy, round structures with a granular content limited by a single membrane were observed in Acanthamoeba castellanii, Acanthamoeba griffini, Acanthamoeba polyphaga, Acanthamoeba royreba, Balamuthia mandrillaris (Amoebozoa), and Naegleria fowleri (Heterolobosea). Further confirmation for the presence of peroxisomes was obtained by treating trophozoites in situ with diaminobenzidine and hydrogen peroxide, which showed positive reaction products for the presence of catalase. We then performed comparative genomic analyses to identify predicted peroxin homologues in these organisms. Our results demonstrate that a complete set of peroxins-which are essential for peroxisome biogenesis, proliferation, and protein import-are present in all of these amoebae. Likewise, our in silico analyses allowed us to identify a complete set of peroxins in Naegleria lovaniensis and three novel peroxin homologues in Naegleria gruberi. Thus, our results indicate that peroxisomes are present in these three genera of free-living amoebae and that they have a similar peroxin complement despite belonging to different evolutionary lineages.

Peroxisomes in cardiomyocytes and the peroxisome / peroxisome proliferator-activated receptor-loop

It is well established that the heart is strongly dependent on fatty acid metabolism. In cardiomyocytes there are two distinct sites for the β-oxidisation of fatty acids: the mitochondrion and the peroxisome. Although the metabolism of these two organelles is believed to be tightly coupled, the nature of this relationship has not been fully investigated. Recent research has established the significant contribution of mitochondrial function to cardiac ATP production under normal and pathological conditions. In contrast, limited information is available on peroxisomal function in the heart. This is despite these organelles harbouring metabolic pathways that are potentially cardioprotective, and findings that patients with peroxisomal diseases, such as adult Refsum’s disease, can develop heart failure. In this article, we provide a comprehensive overview on the current knowledge of peroxisomes and the regulation of lipid metabolism by PPARs in cardiomyocytes. We also present new experimental evidence on the differential expression of peroxisome-related genes in the heart chambers and demonstrate that even a mild peroxisomal biogenesis defect (Pex11α-/- ) can induce profound alterations in the cardiomyocyte’s peroxisomal compartment and related gene expression, including the concomitant deregulation of specific PPARs. The possible impact of peroxisomal dysfunction in the heart is discussed and a model for the modulation of myocardial metabolism via a peroxisome/PPAR-loop is proposed.

Peroxisomes in brain development and function

Peroxisomes contain numerous enzymatic activities that are important for mammalian physiology. Patients lacking either all peroxisomal functions or a single enzyme or transporter function typically develop severe neurological deficits, which originate from aberrant development of the brain, demyelination and loss of axonal integrity, neuroinflammation or other neurodegenerative processes. Whilst correlating peroxisomal properties with a compilation of pathologies observed in human patients and mouse models lacking all or individual peroxisomal functions, we discuss the importance of peroxisomal metabolites and tissue- and cell type-specific contributions to the observed brain pathologies. This enables us to deconstruct the local and systemic contribution of individual metabolic pathways to specific brain functions. We also review the recently discovered variability of pathological symptoms in cases with unexpectedly mild presentation of peroxisome biogenesis disorders. Finally, we explore the emerging evidence linking peroxisomes to more common neurological disorders such as Alzheimer’s disease, autism and amyotrophic lateral sclerosis. This article is part of a Special Issue entitled: Peroxisomes edited by Ralf Erdmann.

A role for mRNA trafficking and localized translation in peroxisome biogenesis and function?

Peroxisomes are distinct membrane-enclosed organelles involved in the β-oxidation of fatty acids and synthesis of ether phospholipids (e.g. plasmalogens), as well as cholesterol and its derivatives (e.g. bile acids). Peroxisomes comprise a distinct and highly segregated subset of cellular proteins, including those of the peroxisome membrane and the interior matrix, and while the mechanisms of protein import into peroxisomes have been extensively studied, they are not fully understood. Here we will examine the potential role of RNA trafficking and localized translation on protein import into peroxisomes and its role in peroxisome biogenesis and function. Given that RNAs encoding peroxisome biogenesis (PEX) and matrix proteins have been found in association with the endoplasmic reticulum and peroxisomes, it suggests that localized translation may play a significant role in the import pathways of these different peroxisomal constituents.

Estimation of volume densities of hepatocytic peroxisomes in a model fish: catalase conventional immunofluorescence versus cytochemistry for electron microscopy

Accurately accessing changes in the intracellular volumes (or numbers) of peroxisomes within a cell can be a lengthy task, because unbiased estimations can be made only by studies conducted under transmission electron microscopy. Yet, such information is often required, namely for correlations with functional data. The optimization and applicability of a fast and new technical proceeding based on catalase immunofluorescence was implemented herein by using primary hepatocytes from brown trout (Salmo trutta f. fario), exposed during 96 h to two distinct treatments (0.1% ethanol and 50 µM of 17α-ethynylestradiol). The time and cost efficiency, together with the results obtained by stereological analyses, specifically directed to the volume densities of peroxisomes, and additionally of the nucleus in relation to the hepatocyte, were compared with the well-established 3,3'-diaminobenzidine cytochemistry for electron microscopy. With the immuno technique it was possible to correctly distinguish punctate peroxisomal profiles, allowing the selection of the marked organelles for quantification. By both methodologies, a significant reduction in the volume density of the peroxisome within the hepatocyte was obtained after an estrogenic input. The most interesting point here was that the volume density ratios were quite correlated between both techniques. Overall, the immunofluorescence protocol for catalase was evidently faster, cheaper and provided reliable quantitative data that discriminated in the same way the compared groups. After this validation study, we recommend the use of catalase immunofluorescence as the first option for rapid screening of changes of the amount of hepatocytic peroxisomes, using their volume density as an indicator.

Sterol carrier protein 2 regulates proximal tubule size in the Xenopus pronephric kidney by modulating lipid rafts

The kidney is a homeostatic organ required for waste excretion and reabsorption of water, salts and other macromolecules. To this end, a complex series of developmental steps ensures the formation of a correctly patterned and properly proportioned organ. While previous studies have mainly focused on the individual signaling pathways, the formation of higher order receptor complexes in lipid rafts is an equally important aspect. These membrane platforms are characterized by differences in local lipid and protein compositions. Indeed, the cells in the Xenopus pronephric kidney were positive for the lipid raft markers ganglioside GM1 and Caveolin-1. To specifically interfere with lipid raft function in vivo, we focused on the Sterol Carrier Protein 2 (scp2), a multifunctional protein that is an important player in remodeling lipid raft composition. In Xenopus, scp2 mRNA was strongly expressed in differentiated epithelial structures of the pronephric kidney. Knockdown of scp2 did not interfere with the patterning of the kidney along its proximo-distal axis, but dramatically decreased the size of the kidney, in particular the proximal tubules. This phenotype was accompanied by a reduction of lipid rafts, but was independent of the peroxisomal or transcriptional activities of scp2. Finally, disrupting lipid micro-domains by inhibiting cholesterol synthesis using Mevinolin phenocopied the defects seen in scp2 morphants. Together these data underscore the importance for localized signaling platforms in the proper formation of the Xenopus kidney.

Peroxisome determination in optical microscopy: a useful tool derived by a simplification of an old ultrastructural technique

Peroxisomes are able to respond to changes in the cellular environment by adapting their number, morphology and metabolic functions. Recently interest in peroxisomes and their possible roles in physiological and pathological processes have significantly increased. In order to identify peroxisomes, several cytochemical techniques have been developed that require fairly complex procedures or are too expensive to be used for screening. In this paper we show that it is possible to label peroxisomes in several cell lines and in tissues by a simple and cheap technique based on 3,3'-diaminobenzidine (DAB) reactivity. The number of peroxisomes detected with this technique in each cell line was similar to that shown by catalase immunoreaction. The technique appears specific because it was able to detect increased number of peroxisomes after treatment with the specific PPARγ antagonist G3335. Gomori's technique for acid phosphatase activity was used to demonstrate that the DAB positive organelles were not lysosomes. The DAB technique has also been applied to transmission electron microscopy, where it labels round structures that are identified as peroxisomes on the basis of morphology, size and localization. The DAB technique has proved to be specific, simple, fast and cheap, which make it ideal to screen possible peroxisome changes in physiological and pathological conditions.

Photoconversion of CFP to study neuronal tissue with electron microscopy

Being able to use versatile light microscopy on live or fixed samples followed by electron microscopy imaging for high resolution analyses is a challenging goal. The advantage is of course that tracing and localizing fluorescently labeled molecules yields great information about dynamic cellular processes, while electron microscopy of the same sample provides exquisite information about subcellular structures. Here, I describe the straightforward combination of both methods by photoconversion of diaminobenzidine (DAB) through cyan fluorescent protein (CFP) tagged proteins localized to the Golgi apparatus in primary hippocampal neurons.

BODIPY probes to study peroxisome dynamics in vivo

There is a continuing need for bioprobes that are target-specific and combine speed of delivery with maintenance of normal cell behaviour. Towards this end, we are developing small pro-fluorescent molecules that provide such specificity through chemical activation by biomolecules. We have generated a set of BODIPY (boron dipyrromethane) fluorophores, including one that is intrinsically non-fluorescent but on incubation with cells becomes fluorescent at its target site. Addition of these BODIPY probes to plant cells identifies peroxisomes, as verified by co-localization with an SKL-FP construct. Interestingly, in mammalian cells, co-localization with the mammalian peroxisomal marker SelectFX(TM) was not observed. These data suggest fundamental differences in peroxisome composition, development or function between plant and animal cells.

Photooxidation technology for correlated light and electron microscopy

The combination of the capabilities of light microscopical techniques with the power of resolution of electron microscopy along with technical advances has led to a gradual decline of the gap between classical light and electron microscopy. Among the correlative techniques using the synergistic opportunities, photooxidation methods have been established as valuable tools for visualizing cell structures at both light and electron microscopic level. Fluorescent dyes are used to oxidize the substrate diaminobenzidine, which in its oxidized state forms fine granular precipitates. Stained with osmium, the diaminobenzidine precipitates are well discernible in the electron microscope, thus labelling and defining the cellular structures, which at light microscopy level are recorded by fluorescent probes. The underlying photooxidation reaction is based on the excitation of free oxygen radicals that form upon illumination of fluorochromes; this is a central step in the procedure, which mainly influences the success of the method. This article summarizes basic steps of the technology and progresses, shows efforts and elaborated pathways, and focuses on methodical solutions as to the applicability of different fluorochromes, as well as conditions for fine structural localizations of the reaction products.

Electron microscopic visualization of fluorescent signals in cellular compartments and organelles by means of DAB-photoconversion

In this work, we show the photoconversion of the fluorochromes enhanced green fluorescent protein (EGFP), yellow fluorescent protein (YFP), and BODIPY into electron dense diaminobenzidine (DAB)-deposits using the examples of five different target proteins, and the lipid ceramide. High spatial resolution and specificity in the localization of the converted protein-fluorochrome complexes and the fluorochrome-labelled lipid were achieved by methodical adaptations around the DAB-photooxidation step, such as fixation, illumination, controlled DAB-precipitation, and osmium postfixation. The DAB-deposits at the plasma membrane and membranous compartments, such as endoplasmic reticulum and Golgi apparatus in combination with the fine structural preservation and high membrane contrast enabled differential topographical analyses, and allowed three-dimensional reconstructions of complex cellular architectures, such as trans-Golgi-ER junctions. On semithin sections the quality, distribution and patterns of the signals were evaluated; defined areas of interest were used for electron microscopic analyses and correlative microscopy of consecutive ultrathin sections. The results obtained with the proteins golgin 84 (G-84), protein disulfide isomerase (PDI), scavenger receptor classB type1 (SR-BI), and gamma-aminobutyric acid (GABA) transporter 1 (GAT1), on one hand closely matched with earlier immunocytochemical data and, on the other hand, led to new information about their subcellular localizations as exemplified by a completely novel sight on the subcellular distribution and kinetics of the SR-BI, and provided a major base for the forthcoming research.

Close association of centrosomes to the distal ends of the microbody during its growth, division and partitioning in the green alga Klebsormidium flaccidum

Division and partitioning of microbodies (peroxisomes) of the green alga Klebsormidium flaccidum, whose cells contain a single microbody, were investigated by electron microscopy. In interphase, the rod-shaped microbody is present between the nucleus and the single chloroplast, oriented perpendicular to the pole-to-pole direction of the future spindle. A centriole pair associates with one distal end of the microbody. In prophase, the microbody changes not only in shape, from a rodlike to a branched form, but also in orientation, from perpendicular to parallel to the future pole-to-pole direction. Duplicated centriole pairs are localized in close proximity to both distal ends of the microbody. In metaphase, the elongated microbody flanks the open spindle, with both distal ends close to the centriole pair at either spindle pole. The microbody further elongates in telophase and divides after septum formation (cytokinesis) has started. The association between the centrioles and both distal ends of the microbody is maintained throughout mitosis, resulting in the distal ends of the elongated microbody being fixed at the cellular poles. This configuration of the microbody may be favorable for faithful transmission of the organelle during cell division. After cytokinesis is completed, the microbody reverts to the perpendicular orientation by changing its shape. Microtubules radiating from the centrosomes flank the side of the microbody throughout mitosis. The close association of centrosomes and microtubules with the microbody is discussed in respect to the partitioning of the microbody in this alga.

Peroxisomes in human and mouse testis: differential expression of peroxisomal proteins in germ cells and distinct somatic cell types of the testis

The vital importance of peroxisomal metabolism for regular function of the testis is stressed by the severe spermatogenesis defects induced by peroxisomal dysfunction. However, only sparse information is available on the role and enzyme composition of this organelle in distinct cell types of the testis. In the present study, we characterized the peroxisomal compartment in human and mouse testis in primary cultures of murine somatic cells (Sertoli, peritubular myoid, and Leydig cells) and in GFP-PTS1 transgenic mice with a variety of morphological and biochemical techniques. Formerly, peroxisomes were thought to be absent in late stages of spermatogenesis. However, our results obtained by detection of different peroxisomal marker proteins show the presence of these organelles in most cell types in the testis, except for mature spermatozoa. Furthermore, we demonstrate a strong heterogeneity of peroxisomal protein content in various cell types of the human and mouse testis and show marked differences in structure, abundance, and localization of these organelles in spermatids, depending on their maturation. Highest and selective enrichment of the peroxisomal lipid transporters (ABCD1 and ABCD3) as well as ACOX2, the key regulatory enzyme of the beta-oxidation pathway 2 for side chain oxidation of cholesterol, were found in Sertoli cells, whereas Leydig cells were enriched in catalase and ABCD2. Our results suggest a cell type-specific metabolic function of peroxisomes in the testis and point to an important role for peroxisomes in spermiogenesis and in the lipid metabolism of Sertoli cells.

Reactive oxygen species detoxification by catalase is a major determinant of fecundity in the mosquito Anopheles gambiae

The mosquito Anopheles gambiae is a primary vector of Plasmodium parasites in Africa. The effect of aging on reproductive output in A. gambiae females from three strains that differ in their ability to melanize Plasmodium and in their systemic levels of hydrogen peroxide (H2O2), a reactive oxygen species (ROS), was analyzed. The number of eggs oviposited after the first blood meal decreases with age in all strains; however, this decline was much more pronounced in the G3 (unselected) and R (refractory to Plasmodium infection) strains than in the S (highly susceptible to Plasmodium) strain. Reduction of ROS levels in G3 and R females by administration of antioxidants reversed this age-related decline in fecundity. The S and G3 strains were fixed for two functionally different catalase alleles that differ at the second amino acid position (Ser2Trp). Biochemical analysis of recombinant proteins revealed that the Trp isoform has lower specific activity and higher Km than the Ser isoform, indicating that the former is a less efficient enzyme. The Trp-for-Ser substitution appears to destabilize the functional tetrameric form of the enzyme. Both alleles are present in the R strain, and Ser/Ser females had significantly higher fecundity than Trp/Trp females. Finally, a systemic reduction in catalase activity by dsRNA-mediated knockdown significantly reduced the reproductive output of mosquito females, indicating that catalase plays a central role in protecting the oocyte and early embryo from ROS damage.

Subcellular localization of tyrosine-nitrated proteins is dictated by reactive oxygen species generating enzymes and by proximity to nitric oxide synthase

Using high-resolution immuno-electron microscopy the steady-state subcellular distribution of tyrosine-nitrated proteins in different cells and tissues was evaluated. In quiescent eosinophils and neutrophils in the bone marrow intracellular nitrated proteins were mainly restricted to the peroxidase-containing secretory granules. The inducible nitric oxide synthase (iNOS) was expressed in the same granules. Proteins nitrated on tyrosine residues were also abundant in the cytosol of circulating erythrocytes. In the vasculature, nitrated proteins were mainly located in mitochondria and endoplasmic reticulum of the endothelial cells, fibroblasts, and smooth muscle cells. Endogenous nitrated proteins were also found in chondrocytes in cartilage, where it was typically associated with the cytoplasmic interface of the endoplasmic reticulum membrane. Nitrated proteins were also prominent in the peroxisomes of liver hepatocytes and of secretory cells in the lacrimal gland. Challenge of mouse dendritic cells with lipopolysaccharide induced iNOS protein expression in cytosol and peroxisomes and was associated with an increased 3-nitrotyrosine formation in cytosol, mitochondria, and peroxisomes. These data indicate that nitric oxide-dependent protein tyrosine nitration is a physiologically relevant process localized within specific subcellular compartments in close proximity to iNOS and to enzymes capable of peroxidative chemistry and reactive oxygen species production.

Subcellular localization of glyoxylate cycle key enzymes involved in oxalate biosynthesis of wood-destroying basidiomycete Fomitopsis palustris grown on glucose

This study investigated the subcellular localization of key enzymes of the glyoxylate cycle, i.e. isocitrate lyase (ICL; EC 4.1.3.1) and malate synthase (EC 2.3.3.9), that function constitutively in coordination with oxalate biosynthesis of glucose-grownFomitopsis palustris. The ICL purified previously fromF. palustrisis termed FPICL1. Subcellular fractionation analysis of the cell homogenate by the sucrose density-gradient method showed that both key enzymes were present in peroxisomes, whereas acetyl-CoA synthase (EC 6.2.1.1) and oxalate-producing oxaloacetate acetylhydrolase (EC 3.7.1.1) were cytosolic. The peroxisomal localization of FPICL1 was further confirmed by electron microscopic and immunocytochemical analysis with anti-FPICL1 antibody. In addition, the peroxisomal target signal, composed of SKL at the C terminus of the cDNA encoding FPICL1, was found, which also suggests that FPICL1 is peroxisomal. Accordingly, it is postulated that transportation of succinate from peroxisomes to mitochondria, and vice versa, for the transportation of isocitrate or citrate, occurs in glucose-grownF. palustrisfor the constitutive metabolic coordination of the TCA and glyoxylate cycles with oxalate biosynthesis.

Plasmodium falciparum: Discovery of peroxidase active organelles

Staining with 3,3' diaminobenzidine tetrahydrochloride (DAB) is a common method used for the detection of peroxidases. Using this histochemical staining method in conjunction with transmission electron microscopy, we observed oxidation of DAB that was localized to a discrete set of organelles displaying morphological similarity to small (75-90 nm diameter) versions of higher eukaryotic microbodies or peroxisomes. These single membrane bounded organelles were characterized by an asymmetrical matrix capable of oxidizing DAB to an electron dense inclusion. Oxidation of DAB was further found to be dependent upon hydrogen peroxide (H2O2) as a substrate. Given a lack of peroxisomal import proteins and enzymes, it is unlikely that these represent conventional peroxisomes. Rather, they likely represent specialized organelles containing endogenous peroxidase or pseudo-peroxidase activity.

Electron microscopical enzyme histochemistry on unfixed tissues and cells. Bridging the gap between LM and EM enzyme histochemistry

In principle, enzyme histochemistry should be performed on unfixed tissues and cells to avoid inhibition of enzyme activity by chemical fixation. For EM enzyme histochemistry, unfixed tissue specimens include fresh tissue blocks, non-frozen tissue chopper sections, cryostat sections and cell preparations. Studies on localization of enzyme activity at the ultrastructural level in unfixed specimens, be it fresh or frozen, are reviewed here. Preservation of ultrastructural morphology is discussed with special attention to the effects of freezing. It is concluded that unfixed cryostat sections are the best alternative for EM histochemistry of tissues, when interposing a semipermeable membrane in between cryostat section and gelled incubation medium. It is an adequate method to preserve structural integrity of unfixed tissue on the one hand and to avoid inactivation of the enzyme by chemical fixation on the other. For EM cytochemistry on individual cells, a better preservation of ultrastructure may be obtained because freezing can be avoided, but mild pretreatment with a fixative or detergent may be necessary to permeabilize cellular membranes for demonstration of intracellular enzyme activity.

Peroxisome proliferation as a biomarker in environmental pollution assessment

Peroxisome proliferators comprise a heterogeneous group of compounds known for their ability to cause massive proliferation of peroxisomes and liver carcinogenesis in rodents. In recent years it has become evident that other animals may be threatened by peroxisome proliferators, in particular aquatic organisms living in coastal and estuarine areas. These animals are exposed to a variety of pollutants of industrial, agricultural and urban origin which are potential peroxisome proliferators. Both laboratory and field studies have shown that phthalate ester plasticizers, PAHs and oil derivatives, PCBs, certain pesticides, bleached kraft pulp and paper mill effluents, alkylphenols and estrogens provoke peroxisome proliferation in different fish or bivalve mollusc species. The response appears to be mediated by peroxisome-proliferator activated receptors, members of the nuclear receptor family, recently cloned in fish. Based on these results it is proposed that peroxisome proliferation could be used as a biomarker of exposure to a variety of pollutants in environmental pollution assessment. This is illustrated by a case study in which mussels, used worldwide as sentinels of environmental pollution, were transplanted from reference to contaminated areas and vice versa. In mussels native to an area polluted with PAHs and PCBs, peroxisomal acyl-CoA oxidase (AOX) activity and peroxisomal volume density were 2-3 fold and 5-fold higher, respectively, compared to the reference site. When animals were transplanted to the polluted station, with increased concentration of organic xenobiotics, a concomitant significant increase of AOX was recorded. Conversely, in animals transplanted to the cleaner station, AOX activity and peroxisomal volume density decreased significantly. These results indicate that peroxisome proliferation is a rapid (i.e., two days) and reversible response to pollution in mussels. Before peroxisome proliferation can be implemented as a biomarker in biomonitoring programs, a well-defined protocol should be established and validated in intercalibration and quality assurance programmes. Furthermore, the influence of biotic and abiotic factors, some of which are known to affect peroxisome proliferation (season, tide level, interpopulation and interindividual variability), should be taken into consideration. The possible hepatocarcinogenic effects as well as the potential adverse effects on reproduction, development, and growth of peroxisome proliferators are unknown in aquatic organisms, thus providing a challenge for future investigations.

A review of morphological techniques for detection of peroxisomal (and mitochondrial) proteins and their corresponding mRNAs during ontogenesis in mice: application to the PEX5-knockout mouse with Zellweger syndrome

In the era of application of molecular biological gene-targeting technology for the generation of knockout mouse models to study human genetic diseases, the availability of highly sensitive and reliable methods for the morphological characterization of the specific phenotypes of these mice is of great importance. In the first part of this report, the role of morphological techniques for studying the biology and pathology of peroxisomes is reviewed, and the techniques established in our laboratories for the localization of peroxisomal proteins and corresponding mRNAs in fetal and newborn mice are presented and discussed in the context of the international literature. In the second part, the literature on the ontogenetic development of the peroxisomal compartment in mice, with special emphasis on liver and intestine is reviewed and compared with our own data reported recently. In addition, some recent data on the pathological alterations in the liver of the PEX5(-/-) mouse with a peroxisomal biogenesis defect are briefly discussed. Finally, the methods developed during these studies for the localization of mitochondrial proteins (respiratory chain complexes and MnSOD) are presented and their advantages and pitfalls discussed. With the help of these techniques, it is now possible to identify and distinguish unequivocally peroxisomes from mitochondria, two classes of cell organelles giving by light microscopy a punctate staining pattern in microscopical immunohistochemical preparations of paraffin-embedded mouse tissues.

Immunohistochemical analysis of bFGF, TGF-beta1 and catalase in rectus abdominis muscle from cattle foetuses at 180 and 260 days post-conception

The potential for muscle growth depends on myoblast proliferation, which occurs essentially during the first two thirds of the foetal period in cattle. Thereafter, myofibres acquire their contractile and metabolic properties. Proliferation is regulated by molecular growth factors and by the tissue oxidative activity. The aim of this study was the quantification by immunochemistry of basic fibroblast growth factor (bFGF) and transforming growth factor beta 1 (TGF-beta1) and also of enzyme catalase (CAT) activity in rectus abdominis muscle. Samples were collected from cattle foetuses of different growth potential at 180 and 260 days post-conception (dpc). One major conclusion from this work is that protein contents of the muscle tissue bFGF and, to a lower extent, CAT activity decreased with increasing age during the foetal life. No differences were found between the different genotypes of cattle. However, the CAT to bFGF ratio tended to be lower in fast-growing cattle and increased with foetal age. TGF-beta1 did not change with age and was localised mostly at the vascular bed. CAT was detected in smooth and rough reticulum in striated muscles at 180dpc, and additionally in mitochondria at 260dpc. In conclusion, the balance between intracellular growth factors (bFGF and TGF-beta1) and the activity of antioxidant enzyme CAT may participate in the regulation of the transition from myoblast proliferation to differentiation. Thus, increased ratio of CAT to bFGF might be a good index indicating initiation of muscle maturation in cattle foetus prior to birth.

In situ heparin-induced peroxisomal reticulum and biogenesis of peroxisomes in pulmonary intravascular macrophages (PIMs) of caprine lung: an ultrastructural and cytochemical study

Pulmonary intravascular macrophages (PIMs) contain a unique electron-dense globular surface-coat which is sensitive to heparin treatment, halothane anesthesia, and the digestive effect of lipolytic lipase (LPL), suggesting that the coat is predominantly composed of lipoproteins. In the present study, evidence is presented that heparin, when administered intravenously in goats, potentiated both the translocation of the surface-coat into the vacuolar system and the expansion of the Golgi apparatus. Sequentially, these changes were followed by proliferation of peroxisomes in combination with peroxisomal reticulum (PR), a transient precursor of this organelle. The peroxisomes, as well as PR, reacted positively for catalase after aldehyde fixation and 3,3'-diaminobenzidine (DAB) staining. In addition to their role as phagocytes, the ultrastructural and cytochemical detection of peroxisomes suggests a functional capacity of the PIMs, which may be adaptable to the circulating level of free fatty acids (FAAs).

Endothelial apoptosis as the primary lesion initiating intestinal radiation damage in mice

Gastrointestinal (GI) tract damage by chemotherapy or radiation limits their efficacy in cancer treatment. Radiation has been postulated to target epithelial stem cells within the crypts of Lieberkühn to initiate the lethal GI syndrome. Here, we show in mouse models that microvascular endothelial apoptosis is the primary lesion leading to stem cell dysfunction. Radiation-induced crypt damage, organ failure, and death from the GI syndrome were prevented when endothelial apoptosis was inhibited pharmacologically by intravenous basic fibroblast growth factor (bFGF) or genetically by deletion of the acid sphingomyelinase gene. Endothelial, but not crypt, cells express FGF receptor transcripts, suggesting that the endothelial lesion occurs before crypt stem cell damage in the evolution of the GI syndrome. This study provides a basis for new approaches to prevent radiation damage to the bowel.

Femtosecond near-infrared laser pulses elicit generation of reactive oxygen species in mammalian cells leading to apoptosis-like death

Two-photon excitation-based near-infrared (NIR) laser scanning microscopy is currently emerging as a new and versatile alternative to conventional confocal laser scanning microscopy, particularly for vital cell imaging in life sciences. Although this innovative microscopy has several advantages such as highly localized excitation, higher penetration depth, reduced photobleaching and photodamage, and improved signal to noise ratio, it has, however, recently been evidenced that high-power NIR laser irradiation can drastically inhibit cell division and induce cell death. In the present study we have investigated the cellular responses of unlabeled rat kangaroo kidney epithelium (PtK2) cells to NIR femtosecond laser irradiation. We demonstrate that NIR 170-fs laser pulses operating at 80-MHz pulse repetition frequency and at mean power of > or = 7 mW evoke generation of reactive oxygen species (ROS) such as H2O2 that can be visualized in situ by standard in vivo cytochemical analysis using Ni-3,3'-diaminobenzidine (Ni-DAB) as well as with a recently developed fluorescent probe Jenchrom px blue. The formation of the Ni-DAB reaction product as well as that of Jenchrom was relatively more pronounced when irradiated cells were incubated in alkaline solution (pH 8) than in those incubated in acidic solution (pH 6), suggesting peroxisomal localization of these reaction products. Two-photon time-lapse imaging of the internalization of the cell impermeate fluorescent dye propidium iodide revealed that the integrity of the plasma membrane of NIR irradiated cells is drastically compromised. Visualization of the nuclei with DNA-specific fluorescent probes such as 4',6-diamidino-2-phenylindole 24 h postirradiation further provided tangible evidence that the nuclei of these cells undergo several deformations and eventual fragmentation. That these NIR irradiated cells die by apoptosis has been established by in situ detection of DNA strand breaks using the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling method. Because the reactive oxygen species such as H2O2 and OH* can cause noxious effects such as cell membrane injury by peroxidation of polyunsaturated lipids and proteins and oxidative phosphorylation, and alterations of ATP-dependent Ca2+ pumps, these ROS are likely to contribute to drastic cytological alterations observed in this study following NIR irradiation. Taken together, we have established that NIR laser irradiations at mean power > or = 7 mW delivered at pulse duration time of 170 fs generally used in two- and multiphoton microscopes cause oxidative stress (1) evoking production of ROS, (2) resulting in membrane barrier dysfunction, (3) inducing structural deformations and fragmentation of the nuclei as well as DNA strand breaks, (4) leading to cell death by apoptosis.

Detection of peroxisomal proteins and their mRNAs in serial sections of fetal and newborn mouse organs

We present a protocol for detection of peroxisomal proteins and their corresponding mRNAs on consecutive serial sections of fetal and newborn mouse tissues by immunohistochemistry (IHC) and nonradioactive in situ hybridization (ISH). The use of perfusion-fixation with depolymerized paraformaldehyde combined with paraffin embedding and digoxigenin-labeled cRNA probes provided a highly sensitive ISH protocol, which also permitted immunodetection with high optical resolution by light and/or fluorescence microscopy. Signal enhancement was achieved by the addition of polyvinyl alcohol (PVA) for ISH color development. For IHC, signal amplification was obtained by antigen retrieval combined with biotin-avidin-HRP and Nova Red as substrate or by the catalyzed reporter deposition of fluorescent tyramide. Using this protocol, we studied the developmental changes in localization of the peroxisomal marker enzymes catalase (CAT) and acyl-CoA oxidase 1 (AOX), the key regulatory enzyme of peroxisomal beta-oxidation, at the protein and mRNA levels in mice from embryonic Day 14.5 to birth (P0.5). The mRNA signals for CAT and AOX were detected in sections of complete fetuses, revealing organ- and cell-specific variations. Here we focus on the localization patterns in liver, intestine, and skin, which showed increasing mRNA amounts during development, with the strongest signals in newborns (P0.5). Immunolocalization of the corresponding proteins revealed, in close correlation with the mRNAs, a distinct punctate staining pattern corresponding to the distribution of peroxisomes. (J Histochem Cytochem 49:155-164, 2001)